Brushless DC motors consist of a permanent magnet rotor with a three phase stator winding. Brushless DC motors evolved from conventional DC motors where the function of the brushes is replaced by electronics. Brushless DC motors offer longer life and less maintenance than conventional brush DC motors. Most brushless DC motor designs use Hall-Effect sensors to measure the position of the rotor. Hall-Effect sensors provide the absolute position information required to commutate the motor. Using Hall-Effect sensors provides simple, robust commutation and performance roughly comparable to a brushed DC motor. One of the major barriers limiting the market penetration of brushless DC motors has been the cost of the Hall-Effect sensors in brushless DC motors. The Hall-Effect sensors themselves are not particularly expensive. However, the Hall-Effect assembly adds significant expense to the cost of manufacturing the motor. Hall-Effect transistors also typically require five additional wires which add to the installation costs.
A sensorless, brushless DC motor does not have Hall-Effect sensors. Sensorless, brushless DC motors employ more sophisticated electronics using an alternative scheme to control the commutation of the motor. The most common scheme involves measuring the back-EMF of the motor and using this information to control the commutation of the motor. Most existing control loops for sensorless, brushless DC motors comprise analog control loops for controlling the motor. These analog control loops are not particularly effective at maintaining operation of the sensorless, brushless DC motor within a safe region of operation of the DC motor. When the DC motor operates outside of its safe region, there is a high likelihood of damage to the electronic components of the DC motor. Therefore, there is a need for an improved control system for sensorless, brushless DC motors that enables more efficient control of the DC motor and helps in maintaining operation of the DC motor within a designated safe zone.